1. Field of the Invention
The present invention relates to a method of and hearing aid for enhancing the accuracy of sounds heard by a hearing-impaired listener; more particularly, the present invention relates to a method of and hearing aid for enhancing the accuracy of sounds heard by a hearing-impaired listener by means of modifying the frequency of an input sound.
2. Description of the Related Art
The main concept of the hearing aid is to amplify sounds so as to help a hearing-impaired listener to hear previously-unheard sounds. As a result, the hearing-impaired listener can hear the voice of a speaker without the need for the speaker to raise his or her voice. However, the hearing-impaired listener cannot hear sounds with two specific characteristics: the frequency is too high, or the intensity is too low. For example, the sounds corresponding to the Mandarin phonetic symbols “”, “” and “” have such characteristics that the hearing-impaired listener has trouble hearing them. However, most conventional hearing aids, which only enhance the energy of the overall sound without identifying partial syllables that need to be enhanced, may cause sound distortion in the process of amplification. Related known prior arts regarding improving the sound by processing the frequency are briefly described hereinafter:
U.S. Pat. No. 7,305,100 discloses a “dynamic compression in a hearing aid” mainly used for minimizing a sound delay.
U.S. Pat. No. 4,454,609 discloses a “speech intelligibility enhancement” used for enhancing the consonant sounds of speech with high frequency. The greater the high frequency content relative to the low, the more such high frequency content is boosted. In this known prior art, consonant high frequency sounds are enhanced. However, it is very difficult to detect the occurrence of consonants in daily conversations. Therefore, this known prior art is not applicable for a hearing aid.
U.S. Pat. No. 4,759,071 discloses an “automatic noise eliminator for hearing aids” mainly used for noise elimination. It removes all sounds below a predetermined level and transmits a compressed sound range for all sounds above a predetermined level. The object of this known prior art is different from that of the present invention. Further, it may cause sound distortion after all sounds below the predetermined level are removed.
U.S. Pat. No. 6,577,739 discloses an “apparatus and methods for proportional audio compression and frequency shifting”, which provides an understandable audio signal to listeners who have hearing loss in particular frequency ranges by proportionally compressing the audio signal. However, this known prior art compresses all audio signals, which may result in serious sound distortion.
U.S. Pat. No. 7,609,841 (hereinafter “the '841 patent”) discloses a “frequency shifter for use in adaptive feedback cancellers for hearing aids”, which improves a conventional frequency shifting method by means of applying frequency shifting only to the high frequency portion of the signal (which is shifted alternately upward and or downward), wherein the frequency shifting ratio is less than 6%. Although the frequency shifter of the '841 patent also applies frequency shifting to high frequency signals, it does not increase or decrease the energy of the high frequency signals.
U.S. Pat. No. 7,580,536 (hereinafter “the '536 patent”) discloses a “sound enhancement for hearing-impaired listeners”, which provides a method of enhancing sound heard by a hearing-impaired listener. The method of the '536 patent compresses high frequency sounds with energy greater than a predetermined threshold or shifts the high frequency sounds to a lower frequency range without altering low frequency sounds (such as normal human speaking frequencies). According to the embodiment of the '536 patent, the processed high frequency sounds are at 32 kHz (column 6, line 18), which is not a normal human speaking frequency. Furthermore, the specification of the '536 patent does not disclose the value of the “predetermined threshold”.
Therefore, there is a need to provide a method of and hearing aid for enhancing the accuracy of sounds heard by a hearing-impaired listener that is capable of identifying sounds that need to be enhanced so as to modify the frequency accordingly, thereby mitigating and/or obviating the aforementioned problems. The applicant filed U.S. patent application Ser. No. 13/064,645 (Taiwan Patent Application Serial No. 099141772), which also discloses a “method and hearing aid of enhancing the accuracy of sounds heard by a hearing-impaired listener”, whereas the present invention discloses another novel solution.